This invention is a system and method for the production of an RFID interrogator/reader engineered into a Faraday cage device. It is designed to perform secure interrogating/reading of RFID tagged retail consumer items. One of the functions of the invention is to protect consumers from unauthorized reading of RFID tags which are attached to or embedded within their retail purchases. For example, if an RFID electro magnetic signal is read surreptitiously during the communication process between reader and tag then the information has been effectively “skimmed”. This is the bailiwick of identity thieves and those involved in commercial crime.
An RFID interrogator, also known as an RFID reader, is an electronic device which generates and receives an interrogation signal. This signal is electro magnetic in nature. The electro magnetic signals are radiated or harvested by an antenna or an array of antennas which are integral to the interrogator. The functionality of the interrogator includes reading and writing information to RFID tags, also known as transponders. The interrogators can operate on one or a multiple of electro magnetic frequencies. Moreover, the interrogator can perform an anti-collision function effectively distinguishing the reflected signal from tags.
There are basic components which make up an RFID industry standard interrogator. There is a receiver which contains an amplifier and a demodulator. There is also a transmitter that contains a modulator and a power amplifier. Moreover, there is an oscillator, a controller/processor and a send and receive port for an antenna attachment. The purpose of these different components needs to be understood to fully comprehend the import of this invention. When harvesting or capturing an electro magnetic signal from an RFID tag the amplifier expands the electro magnetic signal received in the antenna for the purpose of processing the information contained in the signal. The demodulator extracts the data from the signal which has been harvested by the antenna. The controller/processor processes the data or information received and communicates this data with external networks.
During the process of broadcasting or transmission by the interrogator the oscillator provides the carrier signal to the modulator and a reference signal to the demodulator circuits. The modulator adds the information to the electro magnetic signal which is destined for the transponder. The power amplifier increases the strength of the modulated electro magnetic signal and then routes it to the broadcasting antenna. The function of the antenna is to radiate the electro magnetic signal to the transponder.
There are different methods whereby an interrogator communicates with a tag or transponder depending on whether the tag or transponder is active or passive. The passive and semi-passive tags use a backscatter methodology to deliver information from the tag to the interrogator. The electro magnetic signal radiated by the antenna on the interrogator is demodulated by the tag in order to decode the instructions from the interrogator. The data requested by the interrogator is by way of electro magnetic signal which signal power is used by the tag in order to power a reflective electro magnetic signal containing the information requested by the interrogator back to the interrogator through the modulated signal. Active tag communication is different in that the tag does not reflect the energy of the interrogator. The active tag has its own power source and therefore can transmit information independent of any signal transmitted by the interrogator.
The ability for an interrogator to successfully communicate with a tag is dependent upon two significant factors. Communication is dependent on the distance between the interrogator and the tag. It is also dependent upon the type of tag and its dwell time. The dwell time is the time a tag is in the electro magnetic field of the interrogator. The read range is the maximum distance between the interrogator and the RFID tag whereby the tag can be properly read without diminution in signal.
There are different types of RFID interrogators. There is a fixed type, a hand-held type plus mobile interrogators. The fixed interrogators are usually mounted to walls, doors, or other structures. They can also be integrated into stationary devices, such as conveyor belts or at door portals. The fixed types of interrogators do need an external power source. They can be hard wired or wirelessly connected to a local area network. The hand-held interrogators are usually “gun” shaped and are much smaller than the fixed type. The capabilities of the hand held type are similar to those of the fixed variety. They usually have an antenna built into the unit and are used primarily for exception processing due to their portability and capabilities. They are normally connected directly into the local area network through a wireless connection. The hand-held types are frequently battery powered. The mobile type of interrogators can have PCMCIA cards included in order to connect to laptop PCs. These interrogators can come in different forms such as mobile phones or PDA or vehicle mounted. They are usually powered from an internal battery pack. They are typically wireless in connectivity and are typically mounted on forklifts or clamp trucks. They are manufactured to withstand environmental extremes.
There are RFID interrogation zone considerations which need to be understood to fully comprehend this invention. For example, collision zones occur when there is an RFID system with multiple interrogators operating concurrently which results in electro magnetic signals interfering with each other to the point of negating the signals of some. In this circumstance where readers have overlapping interrogation zones a dense interrogation mode for the reader is necessary. Other strategies to deal with overlapping signals are interrogator synchronization, arbitration, and anti collision protocols. In the dense interrogator mode each interrogator operates at a slightly different frequency so as not to interfere with each other. Furthermore, there is a listen before transmitting protocol known as Listen Before Talk (LBT) which utilizes an algorithm to listen or hear whether another interrogator is using a particular frequency. If an interrogator is heard to be using one particular frequency then the interrogator wishing to operate rolls to another frequency before beginning communication. There is also a system of frequency hopping where the interrogation signals hop between channels within a certain frequency spectrum. For example the interrogation signals would hop between 902 MHz and 928 MHz and they can listen for a signal before using any specific frequency channel. There is often a requirement for interrogator synchronization. This occurs in the circumstance of multiple interrogators operating at the same time in the same place. The electro magnetic signals radiating from the antenna of one interrogator may interfere with the electro magnetic signals radiating from the antennas of other interrogators. This can cause RFID transponders to be misread or not read at all. This type of interference is a function of a number of variables. The size and types of antennas and the output power of the antennas plus the distance between antennas are all critical factors. Synchronization of the interrogators in an RFID system can be accomplished in a number of fashions. Software synchronization uses a common communication bus for all interrogators within a system. In this way the back end controlling host computer is able to administer each interrogator by issuing commands to transmit at separate times for each interrogator. There is also a multiplex method whereby a single interrogator is connected through a switch box to multiple antennas. The interrogator radiation is directed to each antenna separately and in turn ensuring that only one antenna is transmitting at any given time. There is also the shielding method which prevents interference between interrogators by acting as a physical barrier to prevent one tag from being interrogated by two antennas. There are other methods of synchronization. For example there are anti collision software remedies for the problem of interrogator electro magnetic interference with each other. When two or more tags respond simultaneously to an interrogation there is a collision of information. Anti collision processing is the means by which the interrogator distinguishes one tag from the others so that only one tag is processed at a time. Anti collision algorithms are commonly classified as either probabilistic or deterministic. In the probabilistic algorithms, also called asynchronous, the tags respond at randomly generated times. In the deterministic algorithms, also called synchronous, the interrogator sorts through the tags based on their unique identification number.
This Invention incorporates by reference Rodgers application Ser. No. 11/686,946, titled “Precisely tuned RFID antenna”. The Rodgers application describes a method of an RFID antenna manufacturing system whereby the RFID antenna becomes an integral part of an integrated circuit package. The RFID manufacturing system contemplated by the Rodgers application includes photoresist manufacturing techniques to produce a template or die specifically designed to mass produce RFID transponders whereby the chip and antenna becomes one integrated unit. The RFID antenna template or die is precisely tuned, using trimming algorithms and laser technology, to resonate with electro magnetic signal increments of 2 megahertz. According to this system each increment is assigned to a different category in a supply chain. This application reduces the cost, size and weight of prior art RFID transponders. This application reduces signal to noise ratio by producing precisely tuned antennas which provide a gatekeeper function directly correlated to ambient electro magnetic signals.
In using Rodgers application Ser. No. 11/686,946 the different category items at a consumer retail level can be assigned different frequencies in GHz. Each consumer category item can be separated by 2 megahertz through using precisely tuned antennas which are integral to the RFID transponder embedded or attached to each consumer item. In so doing the collision problem is solved in that each category item responds at a slightly different frequency. This is in contrast to one of the prior art methods of interrogator synchronization for coping with electro magnetic signal collision which is to program interrogators to operate at slightly different frequencies as described above. This is the dense interrogation mode type of solution. Furthermore, this Invention increases read rates due to the enclosed reading container. It also eliminates electromagnetic interference within the secure interrogation environment which further contributes to improved read rates.
This Invention is analogous to an RFID Portal. The best way to describe this is by way of a typical application. In a warehouse an RFID portal is best utilized where a forklift is moving inventory through a dock door. As the fork truck moves it is monitored by RFID electro magnetic interrogation. This is accomplished by antennas on the portal. The RFID portal is usually a warehouse dock door. The RFID Portal functions effectively because RFID tags on the case load pallets transported by the forklift truck pass through the signal from the interrogator(s) positioned via antennas on the dock door. The antennas of the portal may be connected to a single RFID interrogator or each antenna can connect to its own individual interrogator. The RFID tags, once energized by the interrogator, require a certain amount of time to power up and respond. It is important that the RF energy which is harvested at the tag remain at a level sufficient to sustain the functionality of the tag until data has been retrieved. This is known as dwell time, or time in beam. If the dwell time is too short the tag may power down prematurely and the read or write operation will not be completed.
This Invention is also analogous to an RFID Tunnel. RFID tunnels are a variation on the portal theme. They are typically used with a conveyor system. Tunnels are often enclosed in RF absorptive material such as anechoic material. This type of system is often referred to as a Faraday cage. Enclosing the tunnel helps contain the RF electro magnetic signal thereby concentrating the RF energy. The RFID Tunnel also reduces the power output requirement of the interrogator system. As with RFID Portals multiple antennas increase the read probability in an RFID tunnel. The enclosure helps to contain and concentrate the interrogation power of the system.
A Faraday cage is an enclosure formed by conducting material, or by a mesh of such material. The enclosure blocks out external static electrical fields. The electrical charges in the enclosing conductor, the metal or metal mesh, repel each other and reside on the outside of the cage. The result is that an external static electrical field will cause the charges to rearrange so as to completely cancel the effect within the interior of the cage. The concept as it relates to the present Invention is to design a structure which acts as an electromagnetic shield used to block radio frequency radiation. The concept is that the shield reduces the coupling of radio waves, electromagnetic fields and electrostatic fields. The amount of reduction depends on the material used in construction, its thickness and the resonating frequencies of the fields of interest. The present Invention proposes a design similar to that of a microwave oven. A typical microwave oven has a window built into it. As part of the glass window there is a metallic screen or mesh. This screen finishes a Faraday cage formed by the oven's metal housing.
The present Invention proposes a Faraday cage, made of insulating glass with a wire mesh embedded into it, to securely interrogate a vulcanized polymer insulated shopping cart, shopping basket or to interrogate individual RFID tagged consumer items. The cage ensures that the RFID electro magnetic signals emanating from the interrogator(s) are contained within the physical limitations of the cage as it is manufactured to the specifications of the shopping cart, shopping basket or individual item basis. These signals are then secure from being skimmed by nefarious entrepreneurs as the air interface is no longer shared, but contained. In other words, the scope of the air interface has been reduced because the conveyance fits snugly within the cage. The meshed glass enclosure allows the consumer to keep an eye on the consumer goods at all times of interrogation while concurrently containing the electro magnetic radiation within the metes and bounds of the Faraday cage type of enclosure. The enclosure blocks electro magnetic interference from outside forces thereby increasing read rates of RFID tags. Furthermore, the Faraday cage enclosure concentrates the RFID interrogation electro magnetic signals into a confined and hermetically sealed space thereby further increasing RFID tag read rates.
As a preferred embodiment, the consumer rolls a shopping cart into the meshed glass stall Faraday cage guided by tracks, similar to the guidance system within a car wash. The entrance door is dropped and sealed after the shopping cart is mechanically pulled into the enclosure. The interrogation takes place in complete electro magnetic privacy while remaining in physical sight of the customer. The shopping cart is automatically rolled out of the other end of the interrogation stall after RFID interrogation is complete to be retrieved by the consumer. The contact less smart card of the consumer can be interrogated simultaneously by placing the contact less smart card in a specially manufactured slot embedded into the shopping cart or shopping basket. In this way, the consumer items and the card are read in the same time and then tallied in a hermetically sealed environment. It is imperative that the shopping cart or shopping basket and card holder be covered with vulcanized polymer to obviate reflectance of metal surfaces. This system is called “Secure Self Scan” by the Inventor. The Inventor is in the process of filing a U.S. Trade Mark Application for “Secure Self Scan.”
Rodgers application Ser. No. 11/733,949, titled “Clip Chip” is incorporated by reference in that it is envisioned by this Invention that the Clip Chip is part and parcel of the consumer items as they ingress and egress the Secure Self Scan system application Ser. No. 11/733,949 is a solution to RFID privacy concerns as these concerns relate to information about customer purchases of consumer goods. The inventive system of this application is known as Clip Chip. It surrenders control of the administration of privacy of personal information from the retailer to the consumer of retail goods. This is accomplished by splitting the RFID transponder into two pieces. On one piece, which is always attached to the consumer item, known as the retained piece, is a unique alpha numeric identifier. On the other piece, which can be detached from the consumer item, known as the detached piece, are the standard EPC data. The two pieces are connected by conductive ink. The consumer is empowered to disable the chip at the point of purchase by tearing the two pieces of the chip in two severing the conductive ink and thereby rendering both pieces of the chip moribund. Furthermore, the Clip Chip system contemplates a method to reconnect the circuit using a secure back end system upon the circumstance of a return of the consumer item for exchange or refund.